<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        .container {
            width: 100%;
            height: 600px;
            background-color: aquamarine;
        }
        .left {
            float: left;
            width: 100px;
            height: 100%;
            margin-left: -100%;
            background-color: olivedrab;
        }
        .main {
            float: left;
            width: 100%;
            height: 100%;
        }
        .inner {
            margin: 0 100px;
            height: 100%;
            background-color: indianred;
        }
        .right {
            float: left;
            width: 100px;
            height: 100%;
            margin-left: -100px;
            background-color: greenyellow;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="left">left</div>
        <div class="main">
            <div class="inner">inner</div>
        </div>
        <div class="right">right</div>
    </div>
</body>
</html>